The present invention relates to the fabrication of a magnetoresistive head for high frequency, high data rate, and high track density applications, and in particular to the fabrication of an inverted magnetoresistive head having the reader portion of the magnetoresistive head fabricated on top of the writer portion of the magnetoresistive head.
Standard magnetoresistive (MR) heads are fabricated with the writer portion fabricated on top of the reader portion. MR heads are used in magnetic storage systems to detect magnetically encoded information from a magnetic storage medium or disc and to write magnetically encoded information to the storage medium. In a read mode, a time dependent magnetic field associated with a transition from a magnetic storage medium directly modulates the resistivity of an MR element. In operation, the change in resistance of the MR element can be detected by passing a sense current through the MR element and measuring the voltage across the MR element. The resulting signal can be used to recover information or data from the magnetic storage medium.
Practical MR elements are typically formed using ferromagnetic metal alloys because of their high magnetic permeability, an example of which is nickel iron (NiFe). A ferromagnetic material is deposited in a thin film upon the surface of an electrically insulated substrate or wafer. Changing magnetic fields originating from the magnetic storage medium produce a change in the magnetization direction of the MR element and thereby change the resistance of the sensor. This phenomenon is called the MR effect.
The element itself comprises a strip of MR material deposited on a magnetic shield layer to form an MR element. A series of depositions and etching processes form an active region from a portion of the MR element. The active region is the area of the MR element that senses changing magnetic fields from the magnetic storage medium. An upper magnetic shield acts as a barrier between the MR element and the surface of the magnetic storage medium to prevent changing magnetic fields associated with transitions passing by the head from linking back to the element. The magnetic shield also serves to protect the element from receiving stray magnetic fields associated with transitions from surrounding magnetic storage media.
Giant MR (GMR) sensors formed from GMR materials are the new line in the family of MR sensors. GMR sensors are formed from GMR elements, which are multi-layered structures. These devices include either layers of ferro-magnetic and non-ferro magnetic films for a similar set of films. Permalloy may or may not be part of the layered pattern. In GMR sensors, the change is resistivity can be in excess of 65 percent.
One problem which affects performance of MR heads is the degree to which surfaces in the head can be fabricated flat or "planarized." In particular, in prior art heads, the top shield of an MR sensor has a dip just above the active region of the MR element. This degrades off track performance. Lack of planarization can also cause an electrical short between various layers of the head, such as between the contacts to the MR element and the top shield or between the top shield and subsequent fabricated layers. In addition, the bottom shield is usually fabricated from sendust or other high permeability magnetic materials, which is relatively rough for a thin film. This relatively rough surface can also cause shorting problems between the bottom shield and the contact film. Attempts at planarizing MR readers have focused on smoothing the bottom shield, planarizing the insulator above the MR sensor, or smoothing the top shield. These steps take additional process time and can limit design flexibility.
Another problem which affects performance of MR heads is that GMR heads are susceptible to interdiffusion among the extremely thin layers of a GMR head during a polymer cure, even when a low temperature polymer cure is utilized. This interdiffusion can destroy the effectiveness of the GMR head.